A judge in Louisiana on Thursday said that Black Lives Matter is a social movement and therefore can’t be sued, dismissing a lawsuit brought by an anonymous police officer.

In his ruling, Chief Judge Brian Jackson, of the U.S. District Court in Baton Rouge, said that the lawsuit against several parties, including Black Lives Matter and DeRay Mckesson, one of the movement’s most prominent supporters, suffered from “numerous deficiencies.”

The officer, of the Baton Rouge Police Department, first filed the suit late last year, arguing that the pair should be held responsible for injuries he suffered while responding to protests in 2016. A rock or piece of concrete thrown at a protest struck him, he said, resulting in loss of teeth and injuries to his jaw, brain and head.

The protest at which the officer was injured, attended by Mr. Mckesson, was held in Baton Rouge in July 2016 amid widespread demonstrations over police shootings of black men. The officer alleged that Mr. Mckesson had helped incite violence at the protest. That month saw five police officers killed at a march against police shootings in Dallas, and three more killed in Baton Rouge.

This is the essential question in what attorneys are calling a first-of-its-kind federal lawsuit, in which a Denver lawyer and a far-left environmental group are asking a judge to recognize the Colorado River as a person.

If successful, it could upend environmental law, possibly allowing the redwood forests, the Rocky Mountains or the deserts of Nevada to sue individuals, corporations and governments over resource pollution or depletion. Future lawsuits in its mold might seek to block pipelines, golf courses or housing developments and force everyone from agriculture executives to mayors to rethink how they treat the environment.

Several environmental law experts said the suit had a slim chance at best. “I don’t think it’s laughable,” said Reed Benson, chairman of the environmental law program at the University of New Mexico. “But I think it’s a long shot in more ways than one.”

The suit was filed Monday in Federal District Court in Colorado by Jason Flores-Williams, a Denver lawyer. It names the river ecosystem as the plaintiff — citing no specific physical boundaries — and seeks to hold the state of Colorado and Gov. John Hickenlooper liable for violating the river’s “right to exist, flourish, regenerate, be restored, and naturally evolve.”

Because the river cannot appear in court, a group called Deep Green Resistance is filing the suit as an ally, or so-called next friend, of the waterway.

It would be ironic if Black Lives Matter continues to enjoy complete impunity from victims of BLM terrorism on the grounds that BLM is not a real thing, while the Colorado River wins a lawsuit over the Bureau of Land Management.